The importance of lithium secondary batteries, nickel-hydride batteries, and other nonaqueous electrolyte secondary batteries as vehicle-mounted power sources and as power sources for personal computers and mobile devices has been increasing in recent years. In particular, lithium secondary batteries, which are lightweight and provide a high energy density, are expected to be preferably used as high-output vehicle-mounted power sources. Lithium secondary batteries undergo charging and discharge through the transit of the Li ion back and forth between a positive electrode and a negative electrode.
In a typical structure for this type of lithium secondary battery, electrodes (a positive electrode and a negative electrode) that carry an electrode mixture layer containing an electrode active material are present on electrode current collectors. The negative electrode current collector used for the negative electrode is, for example, an elongated (this includes sheets and foils) member composed mainly of copper or a copper alloy. The negative electrode active material used for the negative electrode can be exemplified by graphite materials such as natural graphite, synthetic graphic, and amorphous carbons from natural and synthetic graphites. These graphite materials have a layer structure in which a plurality of layers are stacked, and charging and discharge proceed via the insertion of the lithium ion between these layers (into the interlayer) and extraction of the lithium ion from this interlayer.
Patent Literature 1 describes an art in which a graphite powder is solidified and molded into a sheet shape on a substrate (current collector) using a binder and at the same time the (002) plane in the graphite particles in the graphite powder is oriented perpendicular to the plane of the sheet. According to this art, because the (002) plane of the graphite particles present in the graphite powder is oriented in the direction of the positive electrode, the lithium ions that have migrated from the positive electrode can be smoothly inserted into the graphite interlayer.